The instant invention relates generally to chelating resins, and in particular to highly selective chelating resins having alkylaminopyridyl or pyridylimidazolyl functions, and to monomers for their preparation.
As background, polymer resins having ion-exchange properties have long been used to recover metal ions from solution. This recovery technique is advantageous because the resin insolubility and existence as a solid-phase material minimizes any contamination to the treated solution caused by the recovery process. Further, these chelating resins are often suitable for removing metal ions from solutions too dilute for practicable liquid-liquid extractions.
One resin attribute of great interest has been selectivity for particular metal ions. Desirable chelating resins preferentially bind valuable metal ions (e.g. copper and nickel) over less valuable metals ions (e.g. iron) at acid pHs (e.g pHs of 1-4) which most often prevail in hydrometalurgical recovery operations. In this regard, certain resins incorporating alkylaminopyridyl, imidazolyl or pyridylimidazolyl functions have been reported to selectively bind these valuable metal ions.
For instance, U.S. Pat. No. 4,202,944 to Hancock et al. describes resins which incorporate pyridyl, imidazolyl or imidazoline groups. The described resins are prepared by treating a preformed chloromethylated polystyrene matrix with a solution containing the active species of interest. The active species are thereby attached to the chloromethylated polystyrene matrix. Similarly, U.S. Pat. No. 4,031,038 to Grinstead et al. describes chelate-exchange resins capable of selective recovery of copper, nickel, and other valuable metals from acidic aqueous leachate liquor. Again, the resins are prepared by subsequently treating preformed chloromethylated styrene-divinylbenzene copolymer beads, this time with an aminomethylpyridine species.
Resin preparations with chloromethylated polystyrene have been extensively reviewed. See, "Chemical Transformations of Chloromethylated Polystyrene", J. Macromol. Sci. - Rev. Macromol. Chem. Phys., 28, 503-592 (1988); "Chloromethylstyrene: Synthesis, Polymerization, Transformations, Applications", J. Macromol. Sci. - Rev. Macromol. Chem. Phys., 22, 343-407 (1982-83). As these reviews and the above-described patents demonstrate, by far, the predominant preparative approach in the literature and industry has been to react preformed chloromethylated polystyrene beads with a solution of the ligand of interest. In only relatively few instances, monomers incorporating the species of interest have been prepared and polymerized. This approach has seemingly been discarded in many instances, possibly due to difficulties encountered in preparing monomers of sufficient purity to give superior polymer products. For example, distillation, by far the most commonly used purifying method, has not been found to reliably purify monomers incorporating complicated ligands of interest. See, for instance, M. Tomoi, Y. Akada and H. Kakuichi, Macromol. Chem., Rapid Commun., 3, 537-42 (1982). As such, the monomers will contain substantial impurities, as will the polymers derived from them. This can severely impact selectivity of the polymers.
While efforts in the art and industry have provided chelating resins demonstrating some selectivity for certain valuable metals, the primary preparative method has been attachment of ligands to preformed chloromethylated polymer beads. As the applicants' own experience has shown, however, polymers prepared in this fashion have several disadvantages. For instance, the ligand attachment reaction very often gives rise to undesirable byproduct ligands irreversibly attached to the resin which can diminish selectivity. In light of the foregoing, there remains a need and demand for highly selective chelating resins, and to monomers and methods for their preparation. It is this need to which the invention described herein is addressed.